Anode active material for lithium secondary battery, and lithium secondary battery comprising same

ABSTRACT

Disclosed is that an anode active material for a lithium secondary battery, and a lithium secondary battery comprising the same. The anode active material for a lithium secondary battery comprises a composite of a Si-based or Sn-based material and a carbon-based material, a Raman spectrum peak intensity ratio (ID/ID′) of a peak intensity (ID) of a D peak (1360 cm−1 to 1370 cm−1) relative to a peak intensity (ID′) of a D′ peak (1620 cm−1 to 1625 cm−1) of the carbon-based material is 4.5 to 10, a peak intensity ratio (IG/ID) of a peak intensity (IG) of a G peak (1580 cm−1 to 1590 cm−1) relative to a peak intensity (ID) of a D peak (1360 cm−1 to 1370 cm−1) of the carbon-based material is 0.6 to 1.5, and an average diameter (D50) of the Si-based or Sn-based metallic material is 30 nm to 80 nm.

TECHNICAL FIELD

An anode active material for a lithium secondary battery and a lithiumsecondary battery including the same are disclosed.

BACKGROUND ART

In recent years, sizes and weights of mobile information terminals suchas mobile phones, notebooks, and smart phones have been rapidlyincreased, and capacity of batteries used as driving power sources hasbeen demanded.

A lithium secondary battery having a high energy density and a highcapacity is widely used as such a driving power source.

In addition, since mobile information terminals are required to have afunction of a motion picture reproduction function, a game function, andthe like, power consumption has been increased, and meanwhile terminalstends to be miniaturized, so that high capacity and high rate capabilityof the non-aqueous electrolyte secondary battery are more demanded.

In order to meet such demands, attempts have been made to form acomposite of a carbon-based base material conventionally used as ananode and a metal oxide or a metal nanoparticle. However, when metal ormetal oxide nanoparticles are used in an anode, particle deformation dueto expansion/shrinkage may occur, and thus it is difficult to becommercialized at present.

DISCLOSURE Technical Problem

An embodiment provides an anode active material for a lithium secondarybattery having improved cycle-life characteristics.

Another embodiment provides a lithium secondary battery including theanode active material.

Technical Solution

An embodiment provides an anode active material for a lithium secondarybattery including a composite of a Si-based or Sn-based material and acarbon-based material, wherein a Raman spectrum peak intensity ratio(I_(D)/I_(D′)) of a peak intensity (I_(D)) of a D peak (1360 cm⁻¹ to1370 cm⁻¹) relative to a peak intensity (I_(D′)) of a D′ peak (1620 cm⁻¹to 1625 cm⁻¹) of the carbon-based material is 4 to 10, a peak intensityratio (I_(G)/I_(D)) of a peak intensity (I_(G)) of a G peak (1580 cm⁻¹to 1590 cm⁻¹) relative to a peak intensity (I_(D)) of a D peak (1360cm⁻¹ to 1370 cm⁻¹) of the carbon-based material is 0.6 to 1.5, and anaverage diameter (D50) of the Si-based or Sn-based metallic material is30 nm to 80 nm.

The peak intensity ratio (I_(G)/I_(D)) of the peak intensity (I₁₆₂₀) ofthe G peak (1580 cm⁻¹ to 1590 cm⁻¹) relative to the peak intensity ofthe D peak (1360 cm⁻¹ to 1370 cm⁻¹) of the carbon-based material may be0.65 to 1.2.

The Raman spectrum peak intensity ratio (I_(D)/I_(D′)) of the peakintensity (I_(D)) of the D peak (1360 cm⁻¹ to 1370 cm⁻¹) relative to thepeak intensity of the D′ peak (1620 cm⁻¹ to 1625 cm⁻¹) of thecarbon-based material may be 4.5 to 9.0.

The Si-based or Sn-based material may have an average particle diameter(D50) of 40 nm to 60 nm.

The Si-based or Sn-based material may be an alloy further including Fe,Ni, Mg, Na, or a combination thereof.

The carbon-based material may be crystalline carbon.

A mixing ratio of the Si-based or Sn-based material and the carbon-basedmaterial may be a weight ratio of 50:50 to 99:1.

Another embodiment of the present invention provides a lithium secondarybattery including an anode including the anode active material; acathode comprising a cathode active material; and an electrolyte.

Other details of the embodiments of the present invention are includedin the following detailed description.

Advantageous Effects

The anode active material for a lithium secondary battery according toan embodiment may provide a lithium secondary battery having excellentcycle-life characteristics.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a structure of a lithium secondary batteryaccording to an embodiment of the present invention.

FIG. 2 is a SEM photograph of the anode active material preparedaccording to Example 1.

MODE FOR INVENTION

Hereinafter, embodiments of the present invention will be described indetail. However, the present invention is not limited thereto, and thepresent invention is only defined by the scope of the following claims.

An anode active material for a lithium secondary battery according to anembodiment of the present invention includes a composite of a Si-basedor Sn-based material and a carbon-based material.

The carbon-based material may have a vacancy defect and a Sp3 typedefect on its surface. The presence of vacancy defects and Sp3 typedefects may be measured from Raman spectral peak intensities.Particularly, the presence may be known from a Raman spectrum peakintensity ratio (I_(D)/I_(D′)) of a peak intensity (I_(D)) of a D peak(1360 cm⁻¹ to 1370 cm⁻¹) relative to a peak intensity (I_(D′)) of a D′peak (1620 cm⁻¹ to 1625 cm⁻¹) of the carbon-based material, and asuitable presence of such defects is known from a Raman spectrum peakintensity ratio (I_(G)/I_(D)) of a peak intensity (I_(G)) of a G peak(1580 cm⁻¹ to 1590 cm⁻¹) relative to a peak intensity (I_(D)) of a Dpeak (1360 cm⁻¹ to 1370 cm⁻¹).

According to an embodiment of the present invention, the Raman spectrumpeak intensity ratio (I_(D)/I_(D′)) of the peak intensity (I_(D)) of theD peak (1360 cm⁻¹ to 1370 cm⁻¹) relative to the peak intensity (I_(D′))of the D′ peak (1620 cm⁻¹ to 1625 cm⁻¹) of the carbon-based material maybe 4 to 10, and according to another embodiment, 4.5 to 9.0. When theRaman spectrum peak intensity ratio (I_(D)/I_(D′)) is within the ranges,electron density of the carbon-based material may be relaxed, and thedispersibility on the surface may be improved. Also, when the Ramanspectrum peak intensity ratio (I_(D)/I_(D′)) is lower than 4.5, thedefects may be excessively formed and consequently the Raman spectralpeak intensity ratio (I_(G)/I_(D)) may be lowered, which is notdesirable.

The Raman spectrum peak intensity ratio (I_(G)/I_(D)) of the peakintensity (I_(G)) of the G peak (1580 cm⁻¹ to 1590 cm⁻¹) relative to thepeak intensity (I_(D)) of the D peak (1360 cm⁻¹ to 1370 cm⁻¹) of thecarbon-based material may be 0.6 to 1.5, and according to anotherembodiment 0.65 to 1.2. When the Raman spectrum peak intensity ratio(I_(G)/I_(D)) is within the ranges, vacancy defects and Sp3 type defectsexisting on the surface of the carbon-based material may be properlypresent. When the Raman spectrum peak intensity ratio (I_(G)/I_(D))exceeds 1.5, vacancy defects and Sp3 type defects are significantlydeteriorated, Sp3 defects are more likely to be generated than vacancydefects, and the Raman spectral peak intensity ratio (I_(D)/I_(D′)) maybe also increased, which is not desirable.

In addition, when the Raman spectrum peak intensity ratio of thecarbon-based material is within the ranges, cycle-life characteristicsmay be improved and when one of the Raman spectrum peak intensity ratio(I_(D)/I_(D′)) or the peak intensity ratio (I_(G)/I_(D)) is out of theranges, cycle-life characteristics may be deteriorated, which is notdesirable.

In the present specification, the Raman spectrum peak intensity may bemeasured using a laser of about 514 nm wavelength or a laser of about633 nm wavelength, unless it is specifically limited, and according toan embodiment, it may be measured using a laser of about 514 nmwavelength. An interpretation regarding such a Raman spectrum may begenerally classified into a height ratio (intensity ratio) or anintegral area ratio of peaks obtained from the Raman spectrum, and in anembodiment of the present invention, a height ratio may be referred.That is, it may refer to a peak intensity ratio (I_(D)/I_(D′)) of aheight of the peak appearing in D (1360 cm⁻¹ to 1370 cm⁻¹), a peakintensity (I_(D)) relative to the height of the peak appearing in D′(1620 cm⁻¹ to 1625 cm⁻¹), a peak intensity (I_(D′)) and a peak intensityratio (I_(G)/I_(D)) of a height of the peak appearing in G (1580 cm⁻¹ to1590 cm⁻¹), a peak intensity (I_(G)) relative to a height of the peakappearing in D (1360 cm⁻¹ to 1370 cm⁻¹), a peak intensity (I_(D))obtained in the Raman spectrum.

An average particle diameter (D50) of the Si-based or Sn-based materialmay be 30 nm to 80 nm, or 40 nm to 60 nm. When the average particlediameter (D50) of the Si-based or Sn-based material is within theranges, expansion or contraction of the Si-based or Sn-based materialmay be suppressed during charging and discharging of the battery usingthe same, and thus, particle deformation may be suppressed and excellentcycle-life characteristics may be obtained. The average particlediameter (D50) generally refers to a diameter of a particle having acumulative volume of 50 vol % in a particle size distribution, butunless defined otherwise in this specification, it may refer to anaverage of the diameters of 150 Si particles in a SEM photograph.

Thus, in an anode active material according to an embodiment of thepresent invention, when the Raman spectrum peak intensity ratio of thecarbon-based material and the average particle diameter (D50) of theSi-based or Sn-based material are included within the ranges, cycle-lifecharacteristics may be improved and if one of these conditions is notsatisfied, cycle-life characteristics may be deteriorated, which are notdesirable.

The Si-based or Sn-based material may be an alloy further including Fe,Ni, Mg, Na, or a combination thereof.

The carbon-based material may be crystalline carbon. The crystallinecarbon may be unspecified shape, sheet-shaped, flake-shaped,sphere-shaped, or fiber-shaped natural graphite or artificial graphite,or a combination thereof. When the carbon-based material is amorphouscarbon, the Raman spectrum peak intensity ratio according to anembodiment may not be obtained, so that the effect may not be obtained.

A mixing ratio of the Si-based or Sn-based material and the carbon-basedmaterial may be a weight ratio of 50:50 to 99:1, and preferably a weightratio of 70:30 to 90:10. According to another embodiment, when themixing ratio of the Si-based or Sn-based material and the carbon-basedmaterial is within the ranges, sufficient capacity may be increased dueto the Si-based or Sn-based material and long cycle-life characteristicsmay be ensured due to low agglomeration of particles. The Si-based orSn-based material may sufficiently increase capacity and secure a longcycle-life characteristics, since the particle accumulation is small.

The anode active material may be manufactured by the following process.

A process of surface-treating of the carbon-based material is performed.The surface-treating process is explained in detail. First, thecarbon-based material, K₂S₂O₈, and P₂O₅ are mixed in acid.

The carbon-based material may be crystalline carbon. The acid may beH₂SO₄.

A mixing ratio of the carbon-based material and K₂S₂O₈ may be a weightratio of 1:1 to 3:1 and a mixing ratio of the K₂S₂O₈ and P₂O₅ may be aweight ratio of about 1:1. When an amount of the carbon-based materialis out of the range with respect to an amount of K₂S₂O₈, the surfaceoxidation of the carbon-based material may not sufficiently occur, whichis not desirable.

The mixing process may be performed at 40° C. to 90° C. for 2 to 12hours. When the mixing process is performed in the temperature range, anoxidation reaction may be sufficiently performed without a risk ofexplosion due to vapor generation. When the mixing process is performedat a temperature lower than the temperature range, the oxidationreaction does not occur well and it is difficult to form a vacancydefect on the surface and when the process is performed at a temperaturehigher than the temperature range, it is not appropriate because it canbe exploded due to vapor generation.

After the mixing process is completed, it is cooled to produce a primaryproduct.

The primary product is dipped in the acid. In this process, thecarbon-based material is oxidized, and the oxide of the carbon-basedmaterial is formed.

The acid may be HNO₃, H₂SO₄, or a combination thereof. These acids aremore easily penetrated into the carbon-based material and especiallycrystalline carbon, and thus may easily cause oxidization in a basalplane of the carbon-based material, particularly the crystalline carbonthan other acids and may easily form vacancy defect. When it is not easyto be penetrated into the crystalline carbon, oxidation occurs mainly atedges of the crystalline carbon to causes only Sp3 defects, which is notdesirable.

The acid dipping process may be performed at 40° C. to 90° C. for 2hours to 12 hours.

When the reaction is performed at the above-mentioned temperature forthe above-mentioned time, the oxidation reaction may be sufficientlygenerated without a risk of explosion due to vapor generation. When theacid dipping process is performed out of the temperature range, theoxidation reaction may not occur well, or an explosion may occur due tothe vapor generation, and when the acid dipping process is performed outof the time range, it may hardly be reduced in the following process. Inaddition, when the acid dipping process is performed at theabove-mentioned temperature for the above-mentioned time, vacancydefects may not be well formed on the surface of the carbon-basedmaterial, strains may not be effectively reduced, and then agglomerationof particles is much generated in a spray-drying process and thusinappropriately increases particle sizes.

According to the surface treatment process, the vacancy defect and theSp3 defect are formed on the surface of the carbon-based material, andaccordingly, an oxide of the carbon-based material is formed and thusmay relieve electron density and in addition, reduce the chargerelieving and the strain. Accordingly, when the oxide of thecarbon-based material formed through the surface treatment process ismixed with the Si-based or Sn-based material, agglomeration of theSn-based or Sn-based material may be suppressed.

In general, a carbon-based materials, specifically, crystalline carbon,and particularly, a graphene layer has high electron density on thesurface due to a conjugation bond, and in addition, when mixed with aSi-based or Sn-based material, clustering between surface particlesthereof are formed due to a charge strain of a hexagonal plane and thusbring about a non-uniform particle size and reduce dispersibility andaccordingly, increase agglomeration of the Si-based or Sn-basedmaterial. Resultantly, the Si-based or Sn-based material in the anodeactive material may inappropriately have an excessively increased size.

Accordingly, in the present invention, the prepared oxide of thecarbon-based material is mixed with the Si-based or Sn-based material ina solvent. Herein, the oxide of the carbon-based material is mixed withthe Si-based or Sn-based material in a weight ratio of 50:50 to 99:1 andspecifically, 70:30 to 90:10. When the mixing ratio of the oxide of thecarbon-based material with the Si-based or Sn-based material are out ofthe range, for example, a Si amount is too low, desired high capacitymay not be accomplished, while when the Si amount is too high, theagglomeration of particles may be more firmly generated.

The solvent may be water, ethanol, or a combination thereof.

The obtained mixture is spray-dried. This spray-drying process may beperformed at 25° C. to 200° C. For example, the spray-drying process maybe performed by using a spray-drier set at an inlet temperature of 45°C. to 200° C. and an outlet temperature of 80° C. to 120° C.

The spray-dried product is heat-treated at 600° C. to 900° C. under amixed atmosphere of H₂ and Ar to prepare an anode active material. Theheat treatment process may be performed for 2 hours to 12 hours. Whenthe heat treatment is performed within the temperature range, areduction reaction may be sufficiently generated, and surface impuritiesmay be effectively removed.

According to this heat treatment process, the oxide of the carbon-basedmaterial is reduced and formed back into the carbon-based material, andherein, a composite of this carbon-based material with the Si-based orSn-based material is prepared as an anode active material.

In the mixed atmosphere of H₂ and Ar, H₂ and Ar may be mixed in a volumeratio of 1:99 to 10:90.

When the heat treatment process is performed under the mixed atmosphereof H₂ and Ar, the carbon-based material may have the desired Ramanspectrum peak intensity ratio, that is, a Raman spectrum peak intensityratio (I_(D)/I_(D′)) of the peak intensity (I_(D)) of the D peak (1360cm⁻¹ to 1370 cm⁻¹) relative to the peak intensity of the D′ peak (1620cm⁻¹ to 1625 cm⁻¹) in a range of 4.5 to 10, and the peak intensity ratio(I_(G)/I_(D)) of the peak intensity (I_(G)) of the G peak (1580 cm⁻¹ to1590 cm⁻¹) relative to the peak intensity (I_(D)) of the D peak (1360cm⁻¹ to 1370 cm⁻¹) in a range of 0.6 to 1.5.

When the heat treatment process is performed under a H₂ or Ar atmospherealone, a carbon-based material having the desired Raman spectrum peakintensity ratio may not be obtained, and in addition, a Sp3 defect inwhich a surface charge strain decrease of the carbon-based material issmall, is mainly formed on the edge of the carbon-based material, andaccordingly agglomeration of the Si-based or Sn-based material isinappropriately generated. Or even when the heat treatment process isperformed under the mixed atmosphere of H₂ and Ar, but when H₂ and Arare used out of the mixing ratio, for example, when H₂ is used in ahigher amount, there may be a risk of explosion, while when H₂ is usedin a lower ratio, the vacancy defect may be difficult to obtain.

In the prepared anode active material, the carbon-based material mayhave the vacancy defect and the Sp3 defect formed on the surface, whichmay be confirmed from the Raman spectrum peak intensity ratio(I_(D)/I_(D′)) and the Raman spectrum peak intensity ratio(I_(G)/I_(D)).

Another embodiment of the present invention provides a lithium secondarybattery including an anode including the anode active material, acathode comprising a cathode active material, and an electrolyte.

The anode includes an anode active material layer and a currentcollector supporting the anode active material layer.

In the anode active material layer, an amount of the anode activematerial may be 95 wt % to 99 wt % based on a total amount of the anodeactive material layer.

In an embodiment of the present invention, the anode active materiallayer may include a binder, and optionally a conductive material. In theanode active material layer, an amount of the binder may be 1 wt % to 5wt % based on a total amount of the anode active material layer. Whenthe conductive material is further included, 90 wt % to 98 wt % of theanode active material, 1 wt % to 5 wt % of the binder, and 1 wt % to 5wt % of the conductive material may be used.

The binder serves to adhere the anode active material particles to eachother and to adhere the anode active material to a current collector.The binder includes a non-aqueous binder, an aqueous binder, or acombination thereof.

The non-aqueous binder may be selected from polyvinylchloride,carboxylated polyvinylchloride, polyvinylfluoride, an ethyleneoxide-containing polymer, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, polyamideimide, polyimide, or a combination thereof.

The aqueous binder may be selected from a styrene-butadiene rubber, anacrylated styrene-butadiene rubber (SBR), an acrylonitrile-butadienerubber, an acrylic rubber, a butyl rubber, polypropylene, an ethylenepropylene copolymer, polyepichlorohydrine, polyphosphazene,polyacrylonitrile, polystyrene, ethylenepropylenedienecopolymer,polyvinylpyridine, chlorosulfonated polyethylene, latex, a polyesterresin, an acrylic resin, a phenolic resin, an epoxy resin, polyvinylalcohol, or a combination thereof.

When the aqueous binder is used as the anode binder, a cellulose-basedcompound may be further used to provide viscosity as a thickener. Thecellulose-based compound includes one or more of carboxylmethylcellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkalimetal salts thereof. The alkali metal may be Na, K, or Li. Such athickener may be included in an amount of 0.1 parts by weight to 3 partsby weight based on 100 parts by weight of the anode active material.

The conductive material is included to provide electrode conductivityand any electrically conductive material may be used as a conductivematerial unless it causes a chemical change in a battery. Examples ofthe conductive material include a carbon-based material such as naturalgraphite, artificial graphite, carbon black, acetylene black, ketjenblack, a carbon fiber, and the like; a metal-based material of a metalpowder or a metal fiber including copper, nickel, aluminum, silver, andthe like; a conductive polymer such as a polyphenylene derivative; or amixture thereof.

The current collector may include one selected from a copper foil, anickel foil, a stainless steel foil, a titanium foil, a nickel foam, acopper foam, a polymer substrate coated with a conductive metal, and acombination thereof.

The cathode may include a positive current collector and a cathodeactive material layer formed on the positive current collector. Thecathode active material may include lithiated intercalation compoundsthat reversibly intercalate and deintercalate lithium ions.Specifically, one or more composite oxides of a metal selected fromcobalt, manganese, nickel, and a combination thereof, and lithium may beused. More specific examples may be compounds represented by one of thefollowing chemical formulae. Li_(a)A_(1-b)X_(b)D₂ (0.90≤a≤1.8, 0≤b≤0.5);Li_(a)A_(1-b)X_(b)O_(2-c)D_(c) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05);Li_(a)E_(1-b)X_(b)O_(2-c)D_(c) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05);Li_(a)E_(2-b)X_(b)O_(4-c)D_(c) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05);Li_(a)Ni_(1-b-c)Co_(b)X_(c)D_(α) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2);Li_(a)Ni_(1-b-c)Co_(b)X_(c)O_(2-α)T_(α) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05,0<α<2); Li_(a)Ni_(1-b-c)Co_(b)X_(c)O_(2-α)T₂ (0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05, 0<α<2); Li_(a)Ni_(1-b-c)Mn_(b)X_(c)D_(α) (0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05, 0<α<2); Li_(a)Ni_(1-b-c)Mn_(b)X_(c)O_(2-α)T_(α) (0.90≤a≤1.8,0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li_(a)Ni_(1-b-c)Mn_(b)X_(c)O_(2-α)T₂(0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li_(a)Ni_(b)E_(c)G_(d)O₂(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1);Li_(a)Ni_(b)Co_(c)Mn_(d)G_(e)O₂ (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5,0.001≤e≤0.1); Li_(a)NiG_(b)O₂ (0.90≤a≤1.8, 0.001≤b≤0.1) Li_(a)CoG_(b)O₂(0.90≤a≤1.8, 0.001≤b≤0.1); Li_(a)Mn_(1-b)G_(b)O₂ (0.90≤a≤1.8,0.001≤b≤0.1); Li_(a)Mn₂G_(b)O₄ (0.90≤a≤1.8, 0.001≤b≤0.1);Li_(a)Mn_(1-g)G_(g)PO₄ (0.90≤a≤1.8, 0≤g≤0.5); QO₂; QS₂; LiQS₂; V₂O₅;LiV₂O₅; LiZO₂; LiNiVO₄; Li_((3-f))J₂(PO₄)₃ (0≤f≤2); Li_((3-f))Fe₂(PO₄)₃(0≤f≤2); Li_(a)FePO₄ (0.90≤a≤1.8)

In the chemical formulae, A is selected from Ni, Co, Mn, and acombination thereof; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr,V, a rare earth element, and a combination thereof; D is selected fromO, F, S, P, and a combination thereof; E is selected from Co, Mn, and acombination thereof; T is selected from F, S, P, and a combinationthereof; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and acombination thereof; Q is selected from Ti, Mo, Mn, and a combinationthereof; Z is selected from Cr, V, Fe, Sc, Y, and a combination thereof;and J is selected from V, Cr, Mn, Co, Ni, Cu, and a combination thereof.

The compounds may have a coating layer on the surface, or may be mixedwith another compound having a coating layer. The coating layer mayinclude at least one coating element compound selected from an oxide ofa coating element, a hydroxide of a coating element, an oxyhydroxide ofa coating element, an oxycarbonate of a coating element, and a hydroxylcarbonate of a coating element. The compound for the coating layer maybe amorphous or crystalline. The coating element included in the coatinglayer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As,Zr, or a mixture thereof. The coating layer may be disposed in a methodhaving no adverse influence on properties of a cathode active materialby using these elements in the compound. For example, the method mayinclude any coating method such as spray coating, dipping, and the like,but is not illustrated in more detail since it is well-known in therelated field.

In the cathode, an amount of the cathode active material may be 90 wt %to 98 wt % based on a total weight of the cathode active material layer.

In an embodiment of the present disclosure, the cathode active materiallayer may further include a binder and a conductive material. Herein,each amount of the binder and the conductive material may be 1 wt % to 5wt % based on a total weight of the cathode active material layer.

The binder improves binding properties of cathode active materialparticles with one another and with a current collector. Examples of thebinder may include polyvinyl alcohol, carboxylmethyl cellulose,hydroxypropyl cellulose, diacetyl cellulose, polyvinylchloride,carboxylated polyvinylchloride, polyvinylfluoride, an ethyleneoxide-containing polymer, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, a styrene butadiene rubber, an acrylated styrenebutadiene rubber, an epoxy resin, nylon, and the like, but are notlimited thereto.

The conductive material is included to provide electrode conductivityand any electrically conductive material may be used as a conductivematerial unless it causes a chemical change in a battery. Examples ofthe conductive material include a carbon-based material such as naturalgraphite, artificial graphite, carbon black, acetylene black, ketjenblack, a carbon fiber, and the like; a metal-based material of a metalpowder or a metal fiber including copper, nickel, aluminum, silver, andthe like; a conductive polymer such as a polyphenylene derivative; or amixture thereof.

The current collector may be an aluminum foil, a nickel foil, or acombination thereof, but is not limited thereto.

The electrolyte includes a non-aqueous organic solvent and a lithiumsalt.

The non-aqueous organic solvent serves as a medium for transmitting ionstaking part in the electrochemical reaction of a battery.

The non-aqueous organic solvent may include a carbonate-based,ester-based, ether-based, ketone-based, alcohol-based, or aproticsolvent.

The carbonate-based solvent may include dimethyl carbonate (DMC),diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropylcarbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate(MEC), ethylene carbonate (EC), propylene carbonate (PC), butylenecarbonate (BC), and the like. The ester-based solvent may include methylacetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethyl propionate, decanolide, mevalonolactone, caprolactone,and the like. The ether-based solvent may include dibutyl ether,tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran,tetrahydrofuran, and the like. In addition, the ketone-based solvent maybe cyclohexanone, and the like. The alcohol based solvent may includeethanol, isopropyl alcohol, and the like, and the aprotic solvent mayinclude nitriles such as R-CN (wherein R is a C2 to C20 linear,branched, or cyclic hydrocarbon group, a double bond, an aromatic ring,or an ether bond), and the like, amides such as dimethyl formamide, andthe like, dioxolanes such as 1,3-dioxolane, and the like, sulfolanes,and the like.

The organic solvent may be used alone or in a mixture and when theorganic solvent is used in a mixture, a mixture ratio may be controlledin accordance with a desirable battery performance, which may beunderstood by a person having an ordinary skill in this art.

In addition, the carbonate-based solvent may include a mixture of acyclic carbonate and a chain-type carbonate. In this case, when thecyclic carbonate and the chain-type carbonate may be mixed together in avolume ratio of 1:1 to 1:9, performance of an electrolyte solution maybe enhanced.

The organic solvent may further include an aromatic hydrocarbon-basedorganic solvent in addition to the carbonate-based solvent. Herein, thecarbonate-based solvent and the aromatic hydrocarbon-based organicsolvent may be mixed in a volume ratio of 1:1 to 30:1.

The aromatic hydrocarbon-based organic solvent may be an aromatichydrocarbon-based compound of Chemical Formula 1.

In Chemical Formula 1, R₁ to R₆ are the same or different, and areselected from the group consisting of hydrogen, a halogen, a C1 to C10alkyl group, a haloalkyl group, and a combination thereof.

Specific examples of the aromatic hydrocarbon-based organic solvent maybe selected from the group consisting of benzene, fluorobenzene,1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene,1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene,1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene,1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene,1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene,1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene,2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene,2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene,2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene,2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene,2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene,2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and a combinationthereof.

The electrolyte may further include an additive of vinylene carbonate oran ethylene carbonate-based compound of Chemical Formula 2 as anadditive for improving the cycle-life characteristics.

In Chemical Formula 2, R₇ and R₈ are the same or different and selectedfrom the group consisting of hydrogen, a halogen, a cyano group (CN), anitro group (NO₂), and a fluorinated C1 to C5 alkyl group, provided thatat least one of R₇ and R₈ is selected from a halogen, a cyano group(CN), a nitro group (NO₂), and a fluorinated C1 to C5 alkyl group, andR₇ and R₈ are not simultaneously hydrogen.

Examples of the ethylene-based carbonate-based compound may be difluoroethylenecarbonate, chloroethylene carbonate, dichloroethylene carbonate,bromoethylene carbonate, dibromoethylene carbonate, nitroethylenecarbonate, cyanoethylene carbonate, or fluoroethylene carbonate. Theamount of the additive for improving cycle-life characteristics may beused within an appropriate range.

The lithium salt dissolved in an organic solvent supplies a battery withlithium ions, basically operates the lithium secondary battery, andimproves transportation of the lithium ions between a cathode and ananode. Examples of the lithium salt include at least one supporting saltselected from LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiN(SO₂C₂F₅)₂, Li(CF₃SO₂)₂N,LiN(SO₃C₂F₅)₂, LiC₄F₉SO₃, LiClO₄, LiAlO₂, LiAlCl₄,LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂), wherein, x and y are naturalnumbers, for example an integer ranging from 1 to 20), LiCl, LiI, andLiB(C₂O₄)₂ (lithium bis(oxalato) borate: LiBOB). A concentration of thelithium salt may range from 0.1 M to 2.0 M. When the lithium salt isincluded at the above concentration range, an electrolyte may haveexcellent performance and lithium ion mobility due to optimalelectrolyte conductivity and viscosity.

The lithium secondary battery may further include a separator betweenthe anode and the cathode, depending on a type of the battery. Examplesof a suitable separator material include polyethylene, polypropylene,polyvinylidene fluoride, and multi-layers thereof such as apolyethylene/polypropylene double-layered separator, apolyethylene/polypropylene/polyethylene triple-layered separator, and apolypropylene/polyethylene/polypropylene triple-layered separator.

FIG. 1 is an exploded perspective view of a lithium secondary batteryaccording to one embodiment. The lithium secondary battery according toan embodiment is illustrated as a prismatic battery but is not limitedthereto and may include variously-shaped batteries such as a cylindricalbattery, a pouch battery, and the like.

Referring to FIG. 1, a lithium secondary battery 100 according to anembodiment may include an electrode assembly 40 manufactured by windinga separator 30 disposed between a cathode 10 and an anode 20 and a case50 housing the electrode assembly 40. An electrolyte (not shown) may beimpregnated in the cathode 10, the anode 20, and the separator 30.

Hereinafter, examples of the present invention and comparative examplesare described. These examples, however, are not in any sense to beinterpreted as limiting the scope of the invention.

Example 1

5.0 g of spherical-shaped natural graphite, 2.0 g of K₂S₂O₈, and 2.0 gof P₂O₅ were dissolved in 25 ml of H₂SO₄ at 80° C. and reacted for 4.5hours. Then, a reaction product obtained therefrom was cooled down andfiltered, and the filtered slurry was sufficiently washed with distilledwater and then, dried.

The dried product was dipped in 20 ml of HNO₃ and reacted at 80° C. for4 hours and then, cooled down and filtered, and then, the filteredproduct was sufficiently washed with distilled water and dried toprepare graphite oxide.

The prepared graphite oxide was mixed with nano-silicon having anaverage particle diameter (D50) of 30 nm in a weight ratio of 4:1 in awater solvent to prepare dispersion. The dispersion was spray-dried byusing a spray drier set at an inlet temperature of 150° C. and at anoutlet temperature of 100° C.

Subsequently, a spray-dried precursor obtained through the spray dryingprocess was fired at 700° C. for 2 hours under a mixed atmosphere of H₂and Ar (a volume ratio of 10:90), and the fired product was slowlycooled down to prepare a composite anode active material of graphite andSi. In the prepared composite anode active material, graphite and Siwere mixed in a weight ratio of 4:0.6.

Comparative Example 1

A composite anode active material of graphite and Si was preparedaccording to the same method as Example 1 except that the spray-driedprecursor obtained through the spray drying process was fired at 700° C.for 2 hours under an Ar atmosphere alone.

In the prepared composite anode active material, graphite and Si weremixed in a weight ratio of 4:0.6.

Comparative Example 2

5.0 g of spherical-shaped natural graphite, 2.0 g of K₂S₂O₈, and 2.0 gof P₂O₅ were dissolved in 25 ml of H₂SO₄ at 80° C. and then, reacted for4.5 hours. The obtained reaction product was cooled down and filtered,and then, the filtered slurry was sufficiently washed with distilledwater and dried.

The dried product was dipped in 20 ml of HNO₃ and reacted at 80° C. for4 hours and the obtained product was fired under a different conditionfrom that of Example 1. Specifically, the reaction product was fired at700° C. for 2 hours under an Ar atmosphere. Subsequently, the firedproduct was cooled down and filtered, and the filtered product wassufficiently washed with distilled water and dried to prepare graphiteoxide.

The graphite oxide was mixed with nano-silicon having an averageparticle diameter (D50) of 30 nm in a weight ratio of 4:1 in a watersolvent to prepare dispersion. The dispersion was spray-dried by using aspray drier having set at an inlet temperature of 150° C. and at anoutlet temperature of 100° C.

Subsequently, a spray-dried precursor obtained through the spray dryingprocess was fired at 700° C. for 2 hours under a mixed atmosphere of H₂and Ar (a volume ratio of 10:90), and the fired product was slowlycooled down to prepare a composite anode active material of graphite andSi. In the composite anode active material, graphite and Si were mixedin a weight ratio of 4:0.6.

Comparative Example 3

5.0 g of spherical-shaped natural graphite, 2.0 g of K₂S₂O₈, and 2.0 gof P₂O₅ were dissolved in 25 ml of H₂SO₄ and reacted at a differenttemperature for a different time from those of Example 1. The obtainedreaction product was cooled down and filtered, and the filtered slurrywas sufficiently washed with distilled water and dried.

The dried product was dipped in 20 ml of HNO₃ and reacted at a differenttemperature for a different time from those of Example 1. Specifically,the product was reacted at 45° C. for 1 hour after the dipping and then,cooled down and filtered, and the filtered product was sufficientlywashed with distilled water and dried to prepare graphite oxide.

The prepared graphite oxide was mixed with nano-silicon having anaverage particle diameter (D50) of 30 nm in a weight ratio of 4:1 in awater solvent to prepare dispersion. The prepared dispersion wasspray-dried by using a spray-drier set at an inlet temperature of 150°C. and an outlet temperature of 100° C.

Subsequently, a spray-dried precursor obtained through the spray dryingprocess was fired at 700° C. for 2 hours under a mixed atmosphere of H₂and Ar (a volume ratio of 10:90), and the fired product was slowlycooled down to prepare a composite anode active material of graphite andSi. In the prepared composite anode active material, graphite and Siwere mixed in a weight ratio of 4:0.6.

Comparative Example 4

5.0 g of spherical-shaped natural graphite, 2.0 g of K₂S₂O₈, and 2.0 gof P₂O₅ were dissolved in 25 ml of H₂SO₄ and reacted at 80° C. for 4.5hours. The obtained reaction product was cooled down and filtered, andthe filtered slurry was sufficiently washed with distilled water anddried.

The dried product was dipped in 20 ml of HNO₃ and reacted at 80° C. fora different time from that of Example 1 and then, fired. Specifically,the product was reacted for 8 hours and then, fired at 700° C. for 2hours under an Ar atmosphere, cooled down, and filtered, and thefiltered product was sufficiently washed with distilled water and driedto prepare graphite oxide.

The prepared graphite oxide was mixed with nano silicon having anaverage particle diameter (D50) of 30 nm in a weight ratio of 4:1 in awater solvent to prepare dispersion. The prepared dispersion wasspray-dried by using a spray-drier set at an inlet temperature of 150°C. and an outlet temperature of 100° C.

Subsequently, a spray-dried precursor obtained through the spray dryingprocess was fired at 700° C. for a different time from that of Example 1and then, treated through an additional firing process. Specifically,the spray-dried precursor was fired for 3 hours under a mixed atmosphereof H₂ and Ar (a volume ratio of 10:90) and then, additionally fired at850° C. for 2 hours by increasing a temperature at 5° C./min

The fired product was slowly cooled down to prepare a composite anodeactive material of graphite and Si. In the prepared composite anodeactive material, graphite and Si were mixed in a weight ratio of 4:0.6.

SEM Measurement and EDS (Energy Dispersive X-Ray Spectrometer) MappingImage

A SEM image of the anode active material according to Example 1 (5000times magnified) was measured, and the result was shown in (a) of FIG.2. In addition, EDS of the anode active material was measured, and themapping result of Si was shown in (b) of FIG. 2.

Raman Intensity Ratio

Raman spectra of the anode active materials according to Example 1 andComparative Examples 1 and 2 were measured at 514 nm. In the Ramanspectrum result, the peak intensity ratios (I_(D)/I_(D′)) of the peakintensity (height) of the D peak (1360 cm⁻¹) relative to the peakintensity (height) of the D′ peak (1620 cm⁻¹) and the peak intensityratios (I_(G)/I_(D)) of the peak intensity (height) of the G peak (1580cm⁻¹) relative to the peak intensity (height) of the D peak (1360 cm⁻¹)are shown in Table 1.

Measurement of Si Size

Average particle diameters of 150 Si particles in SEM images as averageparticle diameters of Si included in each anode active materialsaccording to Example 1 and Comparative Examples 1 and 2 were calculated,and the results are shown in Table 1.

Evaluation of Cycle-Life Characteristics

96.5 wt % of each anode active material according to Example 1 andComparative Examples 1 and 2, 2 wt % of a styrene-butadiene rubberbinder, and 1.5 wt % of carboxylmethyl cellulose 1 were mixed in a watersolvent to prepare anode active material slurry. Then, an anode wasmanufactured in a common process of coating the anode active materialslurry on a Cu current collector and then, drying and compressing it.

The anode, a lithium metal counter electrode, and an electrolytesolution were used in a common method to manufacture a half-cell. Theelectrolyte solution was prepared by using a mixed solvent of carbonate,ethylmethyl carbonate, and dimethyl carbonate (a volume ratio of 2:1:7)in which 1 M LiPF₆ was dissolved and to which fluoroethylene carbonatewas added. In the electrolyte solution, the fluoroethylene carbonate wasused in an amount of 5 wt % based on 100 wt % of the mixed solvent.

The half-cell was 500 times charged at 0.5 C and discharged at 0.5 C andat 25° C. to measure discharge capacity. Discharge capacity ratios ofthe half-cells of discharge capacity at the 500^(th) cycle relative todischarge capacity at the 1^(st) cycle were calculated, and the resultsare shown in Table 1.

TABLE 1 Example Comparative Comparative Comparative Comparative 1Example 1 Example 2 Example 3 Example 4 I_(D)/I_(D′) 5.2 8.4 12 18 4.3I_(G)/I_(D) 0.7 0.58 0.34 3.2 0.56 Si average 52 85 300 312 180 particlediameter (D50, nm) Cycle-life 80 69 less than 50 less than 50 57%characteristics (sharply (sharply (%) decreased) decreased)

As shown in Table 1, the half-cell using the anode active material ofExample 1 showed excellent cycle-life characteristics compared withhalf-cells respectively using those of Comparative Examples 1 to 4. Thereason is that the anode active material according to Example 1 showedpeak intensity ratios (I_(D)/I_(D′)) and (I_(G)/I_(D)) in each range of4.5 to 10 and 0.6 to 1.5 and an average particle diameter (D50) of Siincluded in the anode active material in a range of 40 nm to 65 nm,while the anode active materials according to Comparative Examples 1 to4 showed peak intensity ratios (I_(G)/I_(D)) out of the range of 0.6 to1.5, and the anode active materials according to Comparative Examples 2to 4 showed peak intensity ratios (I_(D)/I_(D′)) out of the range of 4.5to. 10.

In particular, the anode active materials of Comparative Examples 2 and3 having peak intensity ratios (I_(D)/I_(D′)) of greater than 10 weredrastically reduced in cycle-life characteristics and greatly decreasedto less than 50%.

In addition, since the anode active material of Comparative Example 1was prepared by performing a heat treatment under an Ar atmosphere inthe preparation, a Sp3 defect was mainly formed, and accordingly, Si'swere agglomerated and showed an increased average particle diameter(D50) of 85 nm in the prepared anode active material. Particularly,since the anode active materials of Comparative Examples 2 and 4 wereadditionally dipped in HNO₃ and fired at 700° C. for 2 hours, vacancydefects were not well formed, and the Sp3 defects were mainly formed,and accordingly, Si agglomeration was generated and Si average particlediameters (D50) were greatly increased up to 180 nm to 310 nm.

While this invention has been described in connection with what ispresently considered to be practical example embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. On the contrary, it is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. An anode active material for a lithium secondary battery, comprisinga composite of a Si-based or Sn-based material and a carbon-basedmaterial, wherein a Raman spectrum peak intensity ratio (I_(D)/I_(D′))of a peak intensity (I_(D)) of a D peak (1360 cm⁻¹ to 1370 cm⁻¹)relative to a peak intensity (I_(D′)) of a D′ peak (1620 cm⁻¹ to 1625cm⁻¹) of the carbon-based material is 4.5 to 10, a peak intensity ratio(I_(G)/I_(D)) of a peak intensity (I_(G)) of a G peak (1580 cm⁻¹ to 1590cm⁻¹) relative to a peak intensity (I_(D)) of a D peak (1360 cm⁻¹ to1370 cm⁻¹) of the carbon-based material is 0.6 to 1.5, and an averagediameter (D50) of the Si-based or Sn-based metallic material is 30 to 80nm.
 2. The anode active material for a lithium secondary battery ofclaim 1, wherein the peak intensity ratio (I_(G)/I_(D)) of the peakintensity (I_(G)) of the G peak (1580 cm⁻¹ to 1590 cm⁻¹) relative to thepeak intensity (I_(D)) of the D peak (1360 cm⁻¹ to 1370 cm⁻¹) of thecarbon-based material is 0.6 to 1.5, and an average diameter (D50) ofthe Si-based or Sn-based metallic material is 0.65 to 1.2.
 3. The anodeactive material for a lithium secondary battery of claim 1, wherein theRaman spectrum peak intensity ratio (I_(D)/I_(D′)) of the peak intensity(I_(D)) of the D peak (1360 cm⁻¹ to 1370 cm⁻¹) relative to the peakintensity (I_(D′)) of the D′ peak (1620 cm⁻¹ to 1625 cm⁻¹) of thecarbon-based material is 4.5 to 9.0.
 4. The anode active material for alithium secondary battery of claim 1, wherein an average particlediameter (D50) of the Si-based or Sn-based material is 40 nm to 60 nm.5. The anode active material for a lithium secondary battery of claim 1,wherein the Si-based or Sn-based material is an alloy further comprisingFe, Ni, Mg, Na, or a combination thereof.
 6. The anode active materialfor a lithium secondary battery of claim 1, wherein the carbon-basedmaterial is crystalline carbon.
 7. The anode active material for alithium secondary battery of claim 1, wherein a mixing ratio of theSi-based or Sn-based material and the carbon-based material is a weightratio of 50:50 to 99:1.
 8. A lithium secondary battery, comprising ananode comprising the anode active material of claim 1; a cathodecomprising a cathode active material; and an electrolyte.